Hi all, In my airing cupboard I have a copper water cylinder with the water heated by a boiler downstairs. Now and then the top of the cylinder does not get hot so I bleed the cylinder via a bleed valve on a pipe that runs from about halfway up the cylinder to above the cylinders hight. But all of a sudden now when I open the bleed valve no air or water comes out!!! Any ideas please.

The most obvious fault is the air vent is blocked (It could be a number of other things, but try this first). Remove the valve or cap from the body and see what's there. If it's a rubber seal, you need to remove it and put it back in the cap. If there's a hole, it could be blocked, so insert a long pin in to the valve body and poke around until you hear air rushing out.

When you carry out the above actions, be prepared to hear a sudden ruch of air closely followed by water, which will probably come out of the valve body at some pressure. Put some towels down to soak up water that gets spilled.

It can be a bit worrying as a novice carrying out this sort of task, so you may want to call a heating engineer to help out. Bare in mind, if this goes wrong, you could end up with a water leak.

If you do take on the task, do it while the system is cold. It's difficult to replace a valve when hot water is scalding you.